The selective separation of alkaline salts and ionic species from aqueous media is useful in various chemical, biological, medical, and industrial applications. For example selective separation techniques can be used in the production of commodity materials (e.g., bromine, potassium, etc.) from high salt sources, such as the Dead Sea and the Great Salt Lake. Selective separation is also used in biological processes such as the regulation of taste and the maintenance of osmotic balance in cells. Such separations also can be useful in medical applications, for example, the removal of ions from blood or reducing the uptake of ions from ingested foods. Removing or controlling ion levels in a subject can be useful in the control or treatment of numerous disease conditions including hyperkalemia and hyperphosphatemia, which are often associated with diabetes or renal failure.